1. Field of the Invention
The present invention relates to a control system for an internal combustion engine, and particularly, to a control system for a compression ignition internal combustion engine which burns an air-fuel mixture in a combustion chamber by compressing the air-fuel mixture.
2. Description of the Related Art
Japanese Patent Laid-open No. 2005-171818 (JP '818) discloses a control system for a compression ignition internal combustion engine in which premix combustion is performed. According to the control system disclosed by JP '818, an actual ignition timing of fuel is detected during the premix combustion, and the properties of the fuel in use are determined according to an ignition timing error and differences in the ignition timing errors, the ignition timing error being a difference between the actual ignition timing and a previously set reference ignition timing.
The engine operating region, where the premix combustion is performed, is, for example, a hatched region shown in FIG. 10. The hatched region is comparatively narrow relative to the entire engine operating region. Therefore, an execution timing in determining the fuel property is delayed, wherein the fuel injection is performed at a timing not suitable in view of the fuel property, such that a misfire may occur.